Minimization of Intra-Operative Shaping of Orthopaedic Fixation Plates: A Population-Based Design

In this paper we present a new population-based method for the design of bone fixation plates. Standard pre-contoured plates are designed based on the mean shape of a certain population. We propose a computational process to design implants while reducing the amount of required intra-operative shaping, thus reducing the mechanical stresses applied to the plate. A bending and torsion model was used to measure and minimize the necessary intra-operative deformation. The method was applied and validated on a population of 200 femurs that was further augmented with a statistical shape model. The obtained results showed substantial reduction in the bending and torsion needed to shape the new design into any bone in the population when compared to the standard mean-based plates.

Population-Based Design of Mandibular Plates Based on Bone Quality and Morphology

In this paper we present a new population-based implant design methodology, which advances the state-of-the-art approaches by combining shape and bone quality information into the design strategy. The method enhances the mechanical stability of the fixation and reduces the intra-operative in-plane bending which might impede the functionality of the locking mechanism. The method is presented for the case of mandibular locking fixation plates, where the mandibular angle and the bone quality at screw locations are taken into account. Using computational anatomy techniques, the method automatically derives, from a set of computed tomography images, the mandibular angle and the bone thickness and intensity values at the path of every screw. An optimisation strategy is then used to optimise the two parameters of plate angle and screw position. Results for the new design are presented along with a comparison with a commercially available mandibular locking fixation plate. A statistically highly significant improvement was observed. Our experiments allowed us to conclude that an angle of 126° and a screw separation of 8mm is a more suitable design than the standard 120° and 9mm.

Population-based design of mandibular fixation plates with bone quality and morphology considerations

In this paper we present a new population-based implant design methodology, which advances the state-of-the-art approaches by combining shape and bone quality information into the design strategy. The method may enhance the mechanical stability of the fixation and reduces the intra-operative in-plane bending which might impede the functionality of the locking mechanism. The computational method is presented for the case of mandibular locking fixation plates, where the mandibular angle and the bone quality at screw locations are taken into account. The method automatically derives the mandibular angle and the bone thickness and intensity values at the path of every screw from a set of computed tomography images. An optimization strategy is then used to optimize the two parameters of plate angle and screw position. The method was applied to two populations of different genders. Results for the new design are presented along with a comparison with a commercially available mandibular locking fixation plate (MODUS(®) TriLock(®) 2.0/2.3/2.5, Medartis AG, Basel, Switzerland). The proposed designs resulted in a statistically significant improvement in the available bone thickness when compared to the standard plate. There is a higher probability that the proposed implants cover areas of thicker cortical bone without compromising the bone mineral density around the screws. The obtained results allowed us to conclude that an angle and screw separation of 129° and 9 mm for females and 121° and 10 mm for males are more suitable designs than the commercially available 120° and 9 mm.

Repair of orbital floor fractures using bioresorbable poly-L/DL-lactide plates

To assess the long-term clinical and radiologic findings after insertion of a bioresorbable polylactide plates P(L/DL)LA 70/30 implant (PolyMax) in the repair of orbital floor and wall defects, with special focus on stability and clinical signs of foreign-body reaction.

Coronal plane segmental flexibility in thoracic adolescent idiopathic scoliosis assessed by fulcrum-bending radiographs

Knowledge about segmental flexibility in adolescent idiopathic scoliosis is crucial for a better biomechanical understanding, particularly for the development of fusionless, growth-guiding techniques. Currently, there is lack of data in this field. The objective of this study was, therefore, to compute segmental flexibility indices (standing angle minus corrected angle/standing angle). We compared segmental disc angles in 76 preoperative sets of standing and fulcrum-bending radiographs of thoracic curves (paired, two-tailed t tests, p < 0.05). The mean standing Cobb angle was 59.7 degrees (range 41.3 degrees -95 degrees ) and the flexibility index of the curve was 48.6\% (range 16.6-78.8\%). The disc angles showed symmetric periapical distribution with significant decrease (all p values <0.0001) for every cephalad (+) and caudad (-) level change. The periapical levels +1 and -1 wedged at 8.3 degrees and 8.7 degrees (range 3.5 degrees -14.8 degrees ), respectively. All angles were significantly smaller on the-bending views (p values <0.0001). We noted mean periapical flexibility indices of 46\% (+1), 49\% (-1), 57\% (+2) and 81\% (-2), which were significantly less (p < 0.001) than for the group of remote levels 105\% (+3), 149\% (-3), 231\% (+4) and 300\% (-4). The discal and bony wedging was 60 and 40\%, respectively, and mean values 35 degrees and 24 degrees (p < 0.0001). Their relationship with the Cobb angle showed a moderate correlation (r = 0.56 and 0.45). Functional, radiographic analysis of idiopathic thoracic scoliosis revealed significant, homogenous segmental tethering confined to four periapical levels. Future research will aim at in vivo segmental measurements in three planes under defined load to provide in-depth data for novel therapeutic strategies.

Evidence Based Development of a Novel Lateral Fibula Plate (VariAx Fibula) Using a Real CT Bone Data Based Optimization Process During Device Development

Development of novel implants in orthopaedic trauma surgery is based on limited datasets of cadaver trials or artificial bone models. A method has been developed whereby implants can be constructed in an evidence based method founded on a large anatomic database consisting of more than 2.000 datasets of bones extracted from CT scans. The aim of this study was the development and clinical application of an anatomically pre-contoured plate for the treatment of distal fibular fractures based on the anatomical database. 48 Caucasian and Asian bone models (left and right) from the database were used for the preliminary optimization process and validation of the fibula plate. The implant was constructed to fit bilaterally in a lateral position of the fibula. Then a biomechanical comparison of the designed implant to the current gold standard in the treatment of distal fibular fractures (locking 1/3 tubular plate) was conducted. Finally, a clinical surveillance study to evaluate the grade of implant fit achieved was performed. The results showed that with a virtual anatomic database it was possible to design a fibula plate with an optimized fit for a large proportion of the population. Biomechanical testing showed the novel fibula plate to be superior to 1/3 tubular plates in 4-point bending tests. The clinical application showed a very high degree of primary implant fit. Only in a small minority of cases further intra-operative implant bending was necessary. Therefore, the goal to develop an implant for the treatment of distal fibular fractures based on the evidence of a large anatomical database could be attained. Biomechanical testing showed good results regarding the stability and the clinical application confirmed the high grade of anatomical fit.

Effect of a plasmaelectrolytic coating on the strength retention of in vivo and in vitro degraded magnesium implants

The strength decrease in magnesium implants was studied in vitro and in vivo, with and without a protective plasmaelectrolytic coating. In vivo, degradation was examined by implanting rectangular plates on top of the nasal bone of miniature pigs. The presence of gas pockets in the soft tissue surrounding the implants was evaluated with intermediate X-rays and computed X-ray tomography scans before euthanasia. After 12 and 24weeks of in vivo degradation, the large rectangular plates were removed and mechanically tested in three-point bending. In vitro, identical plates were immersed in simulated body fluid for 4, 8 and 12weeks. In vitro and in vivo results showed that onset of gas release can be delayed by the plasmaelectrolytic coating. Mass loss and strength retention during in vivo degradation is about four times slower than during in vitro degradation for the chosen test conditions. Despite the slow degradation of the investigated WE43 alloy, the occurrence of gas pockets could not be completely avoided. Nevertheless, uniformity of degradation and reliable strength retention make this alloy a prime candidate for the use of magnesium in cranio-maxillofacial surgery.

Treatment of tibial fractures with plates using minimally invasive percutaneous osteosynthesis in dogs and cats

OBJECTIVES: The aim of the here described case series was to develop and evaluate the minimally invasive percutaneous osteosynthesis for the plate fixation of tibial fractures in dogs and cats. METHODS: Six dogs and four cats with shaft fractures of the tibia were treated using minimally invasive percutaneous osteosynthesis. Follow-up radiographs four to six weeks after fracture fixation were evaluated for fracture healing. For the long-term follow-up (minimum 2.4 years), owners were contacted by phone to complete a questionnaire. RESULTS: All fractures healed without the need for a second procedure. Follow-up radiographs obtained after four to six weeks in seven cases showed advanced bony healing with callus formation and filling of the fracture gaps with calcified tissue in all seven. All the patients had a good to excellent long-term result with full limb function. The time needed for regaining full limb use was two to three months. CLINICAL SIGNIFICANCE: Minimally invasive percutaneous osteosynthesis seems to be a useful technique for the treatment of tibial shaft fractures in dogs and cats.

Accelerated hypertrophic chondrocyte kinetics in GDF-7 deficient murine tibial growth plates

The Growth/Differentiation Factors (GDFs) are a subgroup of the Bone Morphogenetic Proteins (BMPs) well known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling molecules, GDF-5, have recently been shown to exhibit a decreased rate of endochondral bone growth in the proximal tibia due to a significantly longer hypertrophic phase duration. GDF-7 is a related family member, which exhibits a high degree of sequence identity with GDF-5. The purpose of the present study was to determine whether GDF-7 deficiency also alters the endochondral bone growth rate in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-7 -/- mice and wild type control littermates were examined. GDF-7 deficiency resulted in a statistically significant increase in growth rate (+26%; p = 0.0084) and rate of cell loss at the chondrosseous junction (+25%; p = 0.0217). Cells from GDF-7 deficient mice also exhibited a significantly shorter hypertrophic phase duration compared to wild type controls (-27%; p = 0.0326). These data demonstrate that, in the absence of GDF-7, the rate of endochondral bone growth is affected through the modulation of hypertrophic phase duration in growth plate chondrocytes. These findings further support a growing body of evidence implicating the GDFs in the formation, maturation, and maintenance of healthy cartilage.

Altered hypertrophic chondrocyte kinetics in GDF-5 deficient murine tibial growth plates

The growth/differentiation factors (GDFs) are a subgroup of the bone morphogenetic proteins best known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling proteins, GDF-5, exhibit numerous skeletal abnormalities, including shortened limb bones. The primary aim of this study was determine whether GDF-5 deficiency would alter the growth rate in growth plates from the long bones in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-5 -/- mice and control littermates were examined. GDF-5 deficiency resulted in a statistically significant reduction in growth rate (-14%, p=0.03). The effect of genotype on growth rate was associated with an altered hypertrophic phase duration, with hypertrophic cells from GDF-5 deficient mice exhibiting a significantly longer phase duration compared to control littermates (+25%, p=0.006). These data suggest that one way in which GDF-5 might modulate the rate of endochondral bone growth could be by affecting the duration of the hypertrophic phase in growth plate chondrocytes.